We are studying changes in the translational apparatus which have been found to occur concomitantly with the yeast hyphal dimorphism of Mucor racemosus. Among the physical changes which are known to occur, including alterations of the pattern of methylation of ribosomal RNA, changes in some isoaccepting tRNA species and an alteration in the phosphorylation of ribosomal proteins, we have also discovered a dramatic change in the rate of polypeptide chain elongation as a function of hyphal development. Through the isolation of appropriate mutants, we have also determined that some polyamines are also involved in the dimorphic response of the fungus. We will pursue the relationship of alterations in the translational system to the dimorphic response, as well as the possible involvement of polyamines in the acceleration of polypeptide chain elongation. We will also determine whether or not synthesis of new messenger RNA species is required for the yeast hyphal dimorphism. This will be accomplished by the isolation of messenger RNA, its translation in a wheat germ self-reincorporating system, and the analysis of the polypeptide product by 2-dimensional acrylamide gel electrophoresis.